JP2007144866A - Method and device for humidity-conditioning/drying wood - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drying wood which can prevent the internal crack and deformation of wood and curtail a drying time. <P>SOLUTION: The method includes the first process in which the wood is heated by increasing the temperature of a drying chamber 1 close to 100°C by high temperature steam to make the core part of the wood be heated enough by being kept for a prescribed time, the second process in which the wood is heated at a dry bulb temperature of 110-130°C and at a wet bulb temperature close to 100°C and kept for a prescribed time, the third process in which the heating is stopped before the wood is heated to a prescribed temperature or for a prescribed time, or the wood is dried to have a prescribed water content, and while the temperature is decreased, the water content of the wood is adjusted to dewater the wood, and the fourth process in which the second and third processes are repeated until the average water content of the inside of the wood or the inter-wood is a desired water content. Preferably, the fifth process in which the inside of the drying chamber 1 is kept at a dry bulb temperature of 65-100°C preferably at 80°C and at a wet bulb temperature of 63-98°C preferably at 78°C for a prescribed time, and moisture conditioning is carried out until a water content inclination toward the core part of the wood and the water content of the inter-wood are made approximately uniform is added after the fourth process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is easily discolored due to adhesion of resin components that have flowed out of the wood during drying, such as wood used for building structural materials such as pillars, foundations, beams, girders, especially coniferous and hardwood cored squares and beam girders. The present invention relates to a method and an apparatus for conditioning and drying wood.

The wood used as a building structural material needs to be sufficiently dried over a period of time after felling. However, in order to shorten the drying period, the wood is dried at a high temperature using a wood drying apparatus.
However, due to high running costs (electric power, fuel), low yield (occurrence of cracking and bending due to drying), low productivity (drying time is very long), etc., the column material is about 10 to 20 mm in the surface layer portion. Has been shipped to the market as a desiccant with a moisture content of 20 to 25% by weight and a core part of about 35 to 50% by weight. There was a problem that the yield was low because cracks and bends were easily generated.
In recent years, as a result of countermeasures against these, high-temperature drying technology has progressed, and wood is dried using a wood dryer as shown in Patent Document 1, and although it takes days, cored squares and beam girders are not cracked on the surface, It has become possible to dry with high yield.

The general drying process of the conventional high-temperature drying technique described above is as follows.
1st process (temperature rising / humidifying process): wood is carried into the drying chamber, and 10 to 24 hours until the core inside the wood (hereinafter abbreviated as “inside of the material”) reaches a temperature of 96 to 98 ° C. Steam with high temperature steam and heat.
Second step (high-temperature heating step): Heating the drying chamber with a heater to raise the dry bulb temperature to about 120 ° C, and at the same time, exhausting part of the steam to the outside (forced dehumidification) to prevent cracking of the wood Meanwhile, the wood surface is dried at a high temperature. This state is maintained for approximately 24 hours.
Third step (high-temperature dehydration step): The temperature in the drying chamber is lowered in steps of 5 to 15 ° C. and held at each temperature for 10 to 24 hours. During this time, a part of the steam is discharged to the outside and dried until the wood has a desired moisture content, for example, a moisture content of 15%.
Fourth step (natural cooling step): When the moisture content falls to the desired level, heating and humidification are stopped and natural cooling is performed, and when the temperature of the wood (hereinafter referred to as the material temperature) is sufficiently lowered, the drying chamber Remove wood from
Usually, in the case of a 4 inch square cedar core, it takes 7 to 9 days from carrying wood into the drying chamber.
Japanese Patent Publication No. 4-68550

However, although the surface cracking of the dry wood has been eliminated by the conventional high-temperature drying treatment described above, there are problems of workability and strength reduction due to internal cracks, deformation, etc. of the wood, and further on the appearance due to discoloration that occurs on the wood surface during drying The problem is still not solved.
In recent years, the level of proficiency with construction materials for construction personnel has been lower than before, and almost only precut materials are assembled. In addition, when pre-cut processing is performed, it is difficult for the machine to be applied to a processing machine if the dried wood is deformed, and the processing yield after drying is significantly reduced.
In addition, if there are cracks in the wood, the cracks appear in the machined cross section due to precutting after drying the wood, significantly reducing the strength of the joints, and reducing the strength in the center of the wood that does not appear in the machined cross section. Bring.
In addition, the appearance of wood remains one of the reasons why the discolored high-temperature desiccant is avoided because there remains a tendency to favor the tint of the raw lumber.

  Therefore, the object of the present invention is to prevent internal cracking and deformation of wood, and further discoloration of the wood surface, which are inevitable with conventional high-temperature drying technology, and shorten the drying time compared with conventional high-temperature drying methods. Furthermore, it is an object of the present invention to provide a moisture conditioning drying method and apparatus for wood that can provide a drying material having a very small moisture gradient in the material and excellent in dimensional stability during and after drying.

  The wood moisture conditioning drying method of the present invention is a wood humidity conditioning drying method in which a plurality of woods are carried into a drying chamber and dried by heating, and the dry bulb temperature and wet bulb temperature in the drying chamber (hereinafter referred to as wet and dry temperature). ) Is heated to about 100 ° C. with high-temperature steam, the wood is heated, held for a predetermined time, and adjusted to the temperature up to the wood core, the dry bulb temperature 110-130 2nd step (high temperature heating step) of heating and maintaining wet bulb temperature in the vicinity of 100 ° C. for a predetermined time, heating is stopped until the predetermined temperature or predetermined time or until the wood has a predetermined moisture content, and the temperature is decreasing , A third step (humidity control dehydration step) of dehumidifying the moisture in the material by adjusting the humidity (humidity adjustment), until the average moisture content in the material or the average moisture content between the woods reaches a desired moisture content. 2. Having a fourth step (repeated humidity conditioning dehydration step) that repeats the third step It is characterized.

In the method for conditioning and drying wood according to the present invention, after the fourth step, the drying chamber has a dry bulb temperature of 65 to 100 ° C, preferably 80 ° C, and a wet bulb temperature of 63 to 98 ° C, preferably 78 ° C for a predetermined time. It is desirable to add a fifth step (moisture homogenization step) for holding and adjusting the humidity until the moisture gradient toward the core of each wood and the moisture content between the woods are almost uniform.
Further, after the fifth step, the heating and humidification are stopped, the indoor circulation fan and the high-humidity atmosphere are gradually exhausted, and the air supply / exhaust fan that introduces low-humidity outside air is suppressed to operate. It is desirable to reduce the temperature of the wood while preventing condensation from dripping.

Furthermore, in the method for conditioning and drying wood according to the present invention, the heating means in the first step is high-temperature steam or high-temperature steam and a heater, the heating means in the second and subsequent steps is a heater, and the humidifying means is a steam generator. It is desirable to carry out with the generated normal pressure steam.
In addition, it is desirable that the humidity adjustment and dehydration in the third step is performed by adjusting the amount of steam to be generated so that the temperature difference between the drying and drying becomes a preset numerical value. In addition, it is desirable to adjust the humidity (humidity adjustment) so that the dry / wet temperature difference is not a constant value but decreases as the dry bulb temperature decreases.

  The humidity control and drying apparatus for wood used in the method for humidity conditioning and drying of wood according to the present invention comprises means for supplying high-temperature steam into a drying chamber, means for heating with a heater, and steam at normal pressure that introduces high-temperature steam into the water in the tank. Has a moisture generation device that generates water, a material temperature sensor and moisture content sensor attached to the wood, a moisture content measuring device connected to these sensors to display the moisture content of the wood, and humidity conditioning dehydration drying of the wood are preset It is characterized by having a control device that performs control according to a programmed program.

  According to the moisture conditioning and drying method of wood of the present invention, there is almost no deformation such as internal cracking, twisting, bending, warping and discoloration of the wood surface seen in the dry wood by the conventional high temperature drying method, There is very little moisture gradient. Compared with the conventional method, the shrinkage rate is small, and high quality dry wood is obtained in which the dimensional stability of the wood during and after drying is very high. Furthermore, the moisture content between the dry woods is more uniform than the conventional dry woods, and the drying time can be shortened.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view showing an example of a drying apparatus used in the humidity control drying method for wood according to the present invention.
As shown in FIG. 1, this wood humidity conditioning drying apparatus has a rectangular parallelepiped structure, and the forced drying of wood is performed by carrying a cart 3 loaded with wood 2 from the entrance of the drying chamber 1. .

  The drying chamber 1 usually injects a heating device composed of a heater 4 that raises the room temperature at the top, a boiler provided outside the drying chamber in order to increase the humidity in the drying chamber, and high-temperature steam supplied therefrom. And a circulation device having a circulation fan 6 for circulating the air in the drying chamber, and communicated with an air supply / exhaust fan provided outside the room along the inner wall. Steam is provided with an air supply / exhaust device comprising a pipe 7, and further, a tank 8 provided along the left and right side walls, and a pipe body 9 for supplying high-temperature steam to the water in the tank 8. A water tank 10 is provided at the bottom for receiving a resin liquid or the like flowing out from the wood by drying and discharging it out of the room.

In the steam generator described above, the pipe body 9 is connected to a pipe (not shown) extending from a high-temperature steam generator (not shown) provided outside the drying chamber 1, and is sent out from the high-temperature steam generator. The high-temperature steam is introduced into the tank 8 through the tube body 9, and is ejected into the water in the tank 8 through a small hole provided at an interval in the tube body 9, so that the small hole provided in the top plate of the tank. Then, the steam is discharged into the drying chamber 1 as normal pressure steam.
The timber 2 is loaded on the carriage 3 with a gap through a pier, etc., and after being carried into the drying chamber 1, the timber 2 is heated in a sealed drying chamber at a high temperature in an atmosphere controlled to a desired temperature and humidity. Dried. When the temperature rises, the room atmosphere is circulated in the drying chamber by a powerful circulating fan 6.

  When the wood is brought into the drying chamber, the moisture in the surface layer moves along the grain when heated, and is dehydrated from both ends (wood ends) of the wood. At the same time, the heat conduction into the material deteriorates due to the reduction of the moisture in the surface layer portion, and the moisture remains in the interior, so it is extremely difficult to heat the interior to 100 ° C. or higher. Therefore, even if high temperature drying is continued for a long time, it takes a very long time to lower the desired moisture content. Further, the wood thus dried has a large moisture gradient and shrinkage rate in the material.

  In the present invention, after heating and drying at a high temperature for a predetermined time, the heating is stopped and the humidity is adjusted. That is, by stopping heating and reducing the temperature difference between the wet and dry temperatures, the internal moisture moves along the grain and is discharged, and the moisture gradient in the material is reduced. Again, after heating and drying at high temperature to drain the moisture in the surface layer and causing a moisture gradient, the moisture can be quickly moved to the core of the wood and discharged by repeating heating stop and humidity control. The drying time can be greatly shortened compared to the conventional case.

In the humidity control drying method of the present invention, the depth is changed to one or a plurality of timbers that are standard in the drying chamber, and the material temperature sensor and the moisture content sensor are attached and connected to the moisture content measuring device and the control device. In particular, in the third humidity control and dehydration step, moisture in the material is automatically controlled and dehydrated by a control device (controller). In addition, it is desirable for the moisture content measuring device to display the obtained moisture content together with the temperature and humidity in the material. At the same time, the temperature difference between the wet and dry conditions is obtained, and the humidity is adjusted by adjusting the amount of steam generated based on this difference. This humidity adjustment is performed by the control device in accordance with a program set in advance so as to adjust the humidity in the room.
In this way, by adjusting the wet bulb temperature with the amount of steam generated so that the dry / wet temperature difference decreases as the dry bulb temperature decreases, the movement of moisture in the material to the surface layer can be adjusted, and the material The moisture content inside can be controlled. Further, since the heating is stopped, the humidity is adjusted and dehydrated, the energy saving effect is extremely large, and the running cost can be greatly reduced as compared with the prior art.

Hereinafter, using the drying apparatus shown in FIG. 1, the dehydration drying process of the wood according to the moisture conditioning and drying method of the present invention will be described step by step while comparing with the dehydration drying process of the conventional drying method described above. .
In addition, the target moisture content in the material dried by the humidity control drying method of the present invention is set to 15% by weight in this example.
1st process (temperature rising / humidification process);
After the cart 3 loaded with the wood 2 to be dried is carried into the drying chamber 1, the inside of the drying chamber 1 is sealed, and the wood is heated by raising the wet and dry temperature in the drying chamber to near 100 ° C., preferably 96 to 98 ° C. This state is continued for a predetermined time until the core of the wood reaches that temperature.
The temperature rise in the drying chamber is mainly supplied by spraying (steaming) high-temperature steam from the steam pipe 5, but may be performed using the heater 4 in combination. This increases the wet and dry temperatures.

The above-mentioned predetermined time is that the temperature in the drying chamber rises by 1 to 2 hours due to spraying, but since it is based on the time when the temperature at the center of the wood almost reaches the set temperature, depending on the material, thickness, etc. of the wood Although it is different, it is set with 1 hour as a guide for a thickness of 10 mm toward the core of the wood, and it may be about 5 to 7 hours if it is a normal prismatic material, for example, 4 or 5 inch square.
The first step of the present invention is almost the same as the conventional first step. However, after the temperature of the center of the wood reaches the predetermined temperature after being held for a predetermined time, the first step is automatically performed according to a preset program. Shift to the process.

Second step (high temperature heating step);
After the first step, the vaporization is stopped, the inside of the drying chamber is heated with a heater for a predetermined time to raise the dry bulb temperature to 120 to 130 ° C., and the wet bulb temperature is 100 ° C. with steam generated by introducing high-temperature steam into the water. Keep in the vicinity. The predetermined time is preferably approximately 10 to 24 hours, although it depends on the wood to be dried and the thickness.
The above-described conventional second step and the second step of the present invention have different wet bulb temperatures even in the same high-temperature heat treatment. In the second conventional process, the steam in the drying chamber is forcibly discharged to increase the drying efficiency. Therefore, the energy loss taken out by this is large.

On the other hand, in the second step of the present invention, in order to maintain the wet bulb temperature in the drying chamber at around 100 ° C., that is, about 98-100 ° C., the forced discharge as in the conventional method is not performed. When the humidity cannot be maintained, humidification is performed with steam at normal pressure.
If this humidification is carried out by steaming from the steam pipe 5 as in the conventional method, the surface of the wood may be soiled and discolored. Therefore, the steam generator is used and is disposed in the water in the tank. It is preferable to humidify the steam generated by introducing high-temperature steam into the tube body 9.

3rd process (humidity control dehydration process);
After the high-temperature heat treatment in the second step, heating in the drying chamber is temporarily stopped for a predetermined time or until the predetermined temperature or the wood reaches a predetermined moisture content (hereinafter, represented by the stop of the predetermined time). At this time, the circulating air fan 6 may also be stopped, or the circulating air fan 6 may be operated at a low speed with an inverter and operated with a minimal air volume (slight wind).
When the dry bulb temperature is set to 130 ° C. in the second step, the dry bulb temperature at the time of shifting to the third step is 130 ° C. and the wet bulb temperature is 99.5 to 100 ° C. When the humidification is stopped, the dry bulb temperature falls earlier than the wet bulb temperature, and when the dry bulb temperature is around 100 ° C., the wet bulb temperature becomes around 98.0 to 98.5 ° C. It approaches to the difference of ℃. Thereafter, the wet and dry temperature further decreases, but during that time, when the predetermined time for finishing the third step is reached, the humidity is adjusted by appropriately generating steam according to the dry and wet temperature difference so that the dry and wet temperature difference is as small as possible. As a result, a humidity control effect is generated, the moisture gradient in the material is relaxed, the internal stress is reduced, and the unevenness of the moisture content is reduced. The predetermined time is approximately 10 to 24 hours.

In this way, in the third step, the moisture gradient toward the wood core caused by drying of the wood surface layer in the second step is moved to the wood surface by adjusting the temperature difference between the wet and dry temperatures. be able to. In addition, the humidity adjustment is a real-time dry / wet temperature data obtained from the sensor, which is processed by the control device to obtain the dry / wet temperature difference, and when this value is asymptotic to the set value or zero, A signal is output to the steam generator to humidify, and if it is smaller than the set value, the signal is output to the supply / exhaust fan and discharged.
This is because the wood having a higher moisture content in the core portion has a larger amount of moisture transferred to the surface, and thus the variation in moisture between the woods tends to converge. Thus, the moisture gradient in the material can be relaxed, thereby reducing the unevenness of the moisture content and reducing the stress in the material.
The moisture content of the wood that has undergone this moisture conditioning and dehydration process is reduced to an average of about 50 to 70% on average without causing internal cracks, which was initially 100% to 140%.

4th process (repeated humidity control dehydration process);
The second step and the third step are repeated until the average moisture content of the wood is 15 ± 2 to 3%.
In this step, as in the previous second step, the inside of the drying chamber 1 is again heated with a heater, heated to a dry bulb temperature of 110 to 130 ° C., for example, 130 ° C., and held for 10 to 15 hours. During this time, the wet bulb temperature is maintained at 99.5 to 100 ° C. by humidification. As a result, the surface layer is dried again.
Next, as in the previous third step, by stopping heating for 10 to 24 hours and adjusting the humidity to reduce the temperature difference between the wet and dry, the moisture in the core moves toward the surface, and the moisture gradient in the material is reduced. It becomes smaller and internal stress is relieved. At this time, all of the heating and the circulation fan are stopped or only the heating is stopped, and the circulation fan is operated by the inverter at a low speed and a small air volume.

When this step is finished, the moisture content of the wood, which has been about 50 to 70% at the end of the previous third step, further decreases to about 30 to 50%. By repeating the second and third steps, the water content gradually decreases.
In this fourth step, the water gradient is greatly reduced in the previous step, so that the water can be removed more easily, and the required time is 50-60 compared with the conventional high temperature drying. The productivity is much higher than a dryer with the same volume. In addition, the amount of shrinkage of wood due to drying is performed by repeating dehumidification mainly by stopping the heating and lowering the temperature, so that the internal structure of the wood is not damaged and is about the same as in the case of conventional high-temperature drying. It settles at about 50-60%.

Since the second step performed again in the fourth step is considerably dehydrated in the first and second steps, the surface moisture content of the wood is considerably lowered. For this reason, the wet bulb temperature in the drying chamber cannot often be maintained near the target value of 99 to 100 ° C. Therefore, similarly to the second step, it is preferable that steam is jetted from the steam generator provided in the drying chamber to humidify and maintain the target value.
In addition, when it humidifies by the vaporization of the high temperature steam used for temperature rising / humidification in the 1st process, the discoloration degree of the wood surface will become very strong. On the other hand, humidification with steam is extremely effective in preventing discoloration of wood and is also effective in preventing cracking of wood.

The number of times the second and third steps described above are repeated depends on the type of wood, the target moisture content, and the like, but for example, if the desired moisture content is 15% with a 5 inch square core, Decreasing approximately 3 to 4 times.
Through this fourth step, the average moisture content of the dried wood can be lowered to a desired moisture content, for example, 15%, without causing internal cracking of the dried wood that is observed in conventional high-temperature drying.

5th process (moisture equalization process);
In the fifth step, when the average moisture content of the wood monitored by the sensor has decreased to 15% through the first to fourth steps described above, moisture gradient toward the core of each wood and dry wood In this fifth step, the moisture content of the wood to which the sensor is attached is 15%. This is a process that is performed in order to provide uniform moisture content and provide high quality dry wood with no variation in moisture content. Until the temperature reaches ± 3%, the dry bulb temperature in the drying chamber is set to 65 to 100 ° C., for example, 80 ° C., and the wet bulb temperature is set to 63 to 98 ° C., for example, 78 ° C., and this state is maintained for a predetermined time (10 to 20 hours). maintain. As a result, both high and low moisture contents converge to 15% ± 3%. In addition, it is important to maintain a dry-wet temperature difference at 2-3 degreeC, and it carries out until the moisture gradient in a material or between timbers is equalized. If all the water content is within 15% ± 3% after the fourth step, the fifth step may be omitted.
Even in the fifth step, humidification in the drying chamber is performed with steam at normal pressure using a steam generator in order to prevent soiling and discoloration of the wood surface.

When the moisture content of the wood reaches the target value through the above steps, the controller stops all operations such as heating, humidification, air blowing, etc., natural cooling is performed, and the material temperature is sufficiently lowered. Remove wood from the room.
In addition, when the material size is large, moisture evaporates even during a temperature drop, and indoor condensation may occur and dripping may cause stains on the wood. In order to prevent this, an automatic exhaust cooling process may be employed. This is an optional process as necessary, and is particularly effective for large cross-section materials that require time for temperature drop.

  In this automatic exhaust cooling process, after the first to fourth or first to fifth steps described above, heating and humidification in the drying chamber are stopped, and the circulation fan 6 and the supply / exhaust fan in the chamber are adjusted by an inverter. It operates by. The supply / exhaust fan operates with a reduced air volume so that the room atmosphere can be replaced in about 3 to 5 minutes to prevent sudden temperature and humidity drops, no stress is generated in the material, and there is no product damage. . At this time, the low-humidity outside air whose temperature has been raised through the heat exchanger is introduced into the drying chamber, and at the same time, the indoor high-humidity atmosphere is discharged to the outside. As a result, moisture can be exhausted without rapidly cooling the wood, preventing indoor condensation due to moisture evaporation from the wood during the temperature drop, while preventing indoor condensation from dripping and causing stains on the wood, It is possible to reduce the material temperature.

  The humidity control drying apparatus of the present invention includes a means for supplying high-temperature steam into a drying chamber, a means for heating the drying chamber with a heater, and a steam generator for directing high-temperature steam into water in a tank to generate steam (atmospheric pressure saturated steam). , A material temperature sensor and a moisture content sensor attached to wood, a moisture content measuring device connected to these sensors and displaying the moisture content of wood, and the first to fifth steps described above are controlled in accordance with a preset program Therefore, the time required for drying the wood can be reduced and the unmanned operation can be realized.

  In the initial temperature rising / humidification process, it is necessary to quickly raise the temperature to the core of the wood to a predetermined temperature. However, in the second and subsequent steps, the steam generation apparatus is used, that is, humidification of the room with normal pressure steam generated by introducing high-temperature steam into the water in the tank provided along the side wall of the drying chamber. Is done. This is to prevent the discoloration of the wood from appearing very strongly when directly steaming live steam from the boiler, and humidifying with live steam not only humidifies (increases the wet bulb temperature), but also The dry-bulb temperature also rises due to the large amount of heat retained. In particular, the higher the heat insulation performance of the drying chamber, the more prominent. On the other hand, steam has a much lower amount of heat compared to live steam, so it can be humidified without increasing the dry bulb temperature, and the setting of the dry / wet temperature difference is easy.

A material temperature sensor and a moisture content sensor are connected to the moisture content measuring device, and further connected to the control device via the moisture content measuring device. By automatically recording and displaying these data, it is possible to constantly monitor the state of the wood, and it is also used as real-time data for automatic control. The sensor is set, for example, by inserting a moisture content sensor at a substantially intermediate position in the longitudinal direction of the wood with a prepared hole having a different depth and sealing with heat-resistant caulking.
In addition, the moisture content measuring apparatus incorporates a temperature correction function, and the moisture content measured at each temperature can be corrected and displayed as the moisture content at normal temperature.

A preset program is incorporated in this control device, and the timing of transition to each process is controlled. For this, various transition conditions can be set based on real time data from the moisture content measuring device and each sensor attached to the wood.
For example, various transition conditions may be set such as [average moisture content is 15%], [average moisture content is 15% and maximum moisture content is 18% or less], or [total moisture content is 17% or less]. Can do.
Furthermore, time and material temperature can be added to these conditions. For example, [the state is maintained for 4 hours after the average moisture content reaches 15%], or [the average moisture content is 15% and the maximum moisture content is 18% or less, and the material temperature reaches 104 ° C., It is also possible to set a combination of a plurality of conditions, such as holding the state for 6 hours. In this way, a series of steps can be performed fully automatically.

When a raw material, for example, a 4 inch square material having an initial moisture content of 100 to 150% or more is dried to a moisture content of 15% using the humidity control drying method and apparatus of the present invention, the conventional high temperature drying method takes 7 to 9 days. What was needed was that it could be dried in almost half of the 3.5 days. For this reason, it is excellent in energy saving performance, and the total running cost is about half or less of the conventional method.
Next, an example of the present invention will be described in detail based on the following examples. However, the present invention is not limited to this, and various modes are possible.

When 500 pieces of 132 mm × 132 mm × 3 m cedar core-supported rectangular pillar materials were prepared and the moisture content of these pillar materials was measured before being brought into the drying chamber, the moisture content was approximately 110 to 160%. These timbers were loaded on a carriage with a piercing between them so that the ventilation between the timbers was improved, and carried into the drying chamber shown in FIG.
Of these, six appropriately selected timbers were drilled at different depths at a position 1.5 m in the longitudinal direction from the mouth of the timber, and a set of 6 moisture content sensors for a 12-point moisture meter. Two sets were inserted into the pilot holes and sealed with heat-resistant caulking. Similarly, two sets of 6 temperature sensors were inserted into the holes of the pilot holes opened at different depths, and the temperature was measured with heat-resistant caulking. The pilot holes were drilled at intervals of 30 mm and 60 mm deep from the surface of the wood to the core, and sensors were installed at the bottom of each depth. These sensors were connected to a moisture content meter and a control device provided in the operation room outside the drying room, so that numerical values and graphs were displayed and automatically recorded so that they could be monitored constantly. The sensor cable is a Teflon (registered trademark) cord with extremely high heat and humidity resistance, and the element wire is an oxygen-free copper-silver plated wire.

Thereafter, the door of the wood drying chamber was closed, the drying chamber was sealed, and the drying operation was started.
1st process (temperature rising / humidification process);
First, the wet and dry temperature in the drying chamber was raised to the set temperature of 98 ° C. It took 2 hours to climb. After reaching the set temperature of 98 ° C., it was kept in that state for 6 hours, and the wood core was adjusted to the set temperature.

Second step (high temperature heating step);
After the 1st process, it heated with the heater, the dry-bulb temperature in a drying chamber was heated up to 130 degreeC, and it hold | maintained for 15 hours and performed the high temperature drying process. At that time, steam was generated and adjusted by a steam generator so that the temperature difference between the wet and dry temperatures was approximately 30 ° C., and the wet bulb temperature in the drying chamber was maintained at 99.5 to 100 ° C.

3rd process (humidity control dehydration process);
Subsequently, heating, humidification, and the indoor air blowing fan were stopped, or only the indoor air blowing fan was operated with a minimal air volume (slight wind). During the temperature drop, the water content and the wet / dry temperature were monitored in real time, and the temperature was adjusted with the steam generated by the steam generator so that the difference between the wet and dry temperatures gradually decreased. When 10 hours had passed after the heating was stopped, the dry-wet temperature difference was 2 ° C. at a dry bulb temperature of 82 ° C. and a wet bulb temperature of 80 ° C., and the wood had an average moisture content of 60%. At this time, the sample for evaluation was taken out from the drying chamber, cut, and confirmed. As a result, the moisture gradient in the material was alleviated due to the humidity control effect, and no internal cracking or deformation was observed due to the effect of reducing internal stress.

4th process (repeated humidity control dehydration process);
By performing the second step and the third step for the second time again, the average moisture content of the wood was 40%. In the third time, the average water content was 25%, and in the fourth time, the average water content was 15%. Here, the fourth step was finished, and the process proceeds to the next water homogenization step.

5th process (moisture equalization process);
The dry bulb temperature was maintained at 80 ° C. and the wet bulb temperature at 78 ° C. until all the water content monitored by the sensor was 15% ± 3%. This took about 15 hours.
As a result, a desiccant is obtained in which the stress is removed by relaxation of the moisture gradient and the moisture content is averaged. In this process, the wet bulb temperature was maintained with steam to prevent discoloration.

6th process (automatic dehumidification cooling process);
When the moisture content reaches 15% ± 3%, the heating and humidification in the drying chamber is stopped, and the circulation fan in the room and the air supply / exhaust fan that gradually exhausts the high-humidity atmosphere and introduces low-humidity outside air Operated by adjustment. As a result, during the temperature drop, indoor condensation due to moisture evaporation from the wood was prevented, and the material temperature was lowered while preventing indoor condensation from dripping and causing stains on the wood. When the temperature dropped sufficiently, the wood was taken out of the drying room.
In addition, the wet and dry temperature in each process, the dry and wet temperature difference, the timing of transition between processes, etc. were automatically controlled by the control device based on the real-time data from each sensor according to a preset program.

  According to the humidity control drying method and apparatus for wood of the present invention, it can be used not only for drying wood but also as a humidity control apparatus for all fields that require stable and reliable control of wet bulb temperature using high-temperature steam. , Its industrial utility value is great.

It is a schematic sectional drawing which shows an example of the drying apparatus used for the humidity control drying method of the wood of this invention.

Explanation of symbols

1 Drying room,
2 wood,
3 carts,
4 heaters,
5 Steam pipe,
6 Circulating fan,
7 pipelines,
8 tanks,
9 tube,
10 Aquarium.

Claims (5)

A humidity control drying method for wood in which a plurality of pieces of wood are carried into a drying chamber and dried by heating, and the wood is heated by raising the dry bulb temperature and wet bulb temperature in the drying chamber to near 100 ° C. with high-temperature steam. The first step of holding for a period of time and adjusting to the temperature of the wood core, the second step of heating to a dry bulb temperature of 110 to 130 ° C. and a wet bulb temperature of around 100 ° C. and holding it for a predetermined time, up to a predetermined temperature or Heating is stopped for a predetermined time or until the wood has a predetermined moisture content, and the third step of conditioning and dehydrating the moisture in the wood during the temperature drop, the average moisture content inside the wood or the average moisture content between the woods A method for conditioning and drying wood, comprising a fourth step of repeating the second and third steps until the water content becomes a desired moisture content. After the fourth step, the drying chamber is kept at a dry bulb temperature of 65 to 100 ° C. and a wet bulb temperature of 63 to 98 ° C. for a predetermined time, and the moisture gradient toward the core of the wood and the moisture content between the woods are almost equal. The method for conditioning and drying wood according to claim 1, further comprising a fifth step of performing humidity conditioning until the material is uniformized. After the fifth step, the heating and humidification is stopped, the indoor circulation fan and the high-humidity atmosphere are gradually exhausted, and the air supply / exhaust fan that introduces low-humidity outside air is operated while suppressing the air volume. The method for conditioning and drying wood according to claim 2, wherein the temperature of the wood is lowered while preventing dripping. The heating means in the first step is high-temperature steam or high-temperature steam and a heater, the heating means in the second and subsequent steps is a heater, and the humidifying means is steam at normal pressure generated by a steam generator. The method for conditioning and drying wood according to claim 2. A means for supplying high-temperature steam into the drying chamber, a means for heating with a heater, and a steam generator for directing high-temperature steam into the water in the tank to generate normal-pressure steam, a material temperature sensor and moisture content attached to wood A moisture content measuring device connected to these sensors and displaying the moisture content of the wood, and a control device for controlling the moisture conditioning and dehydration drying of the wood according to a preset program. Humidity conditioning dryer.

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